Metallurgical furnace



METALLURGICAL FURNACE Filed Jan.' 20, 1934 2 Sheets-Sheet l INVENTOR AHLUAM I THOMAS ATTORNEYS Sept. 10, 1935. w. .1. THOMAS 2,013,975

METALLURGICAL FURNACE Filed Jan. 20, 1934 2 Sheets-Sheet 2 INVENTOR \N l LLJAM D", THOMAS ATTORNEYS Patented Sept. 10, 1935 UNITED STATES PATENT OFFICE METALLURGICAL FURNACE Application January 20, 1934, Serial No. 707,451

1 Claim.

This invention relates to metallurgical furnaces and has for an object the provision of improved roasting furnaces and an improved method of constructing such furnaces. More particularly, the invention contemplates the provision of improved multiple hearth furnaces and an improved method of constructing the hearths of multiple hearth furnaces.

A multiple hearth furnace generally comprises a metallic cylinder surrounding a rigid shell of masonry within which are located a plurality of masonry hearths, or floors, disposed one above the other. A hollow central shaft is located within the rigid shell, and extending radially from this shaft are a plurality of rakes, so arranged in tiers that each hearth may be raked by several rakes as the central shaft revolves. Owing to the rotation of the central shaft, it is not feasible to use ll) as a supporting column for the hearths, and because of the rakes which rotate with it, it is impossible to insert columns or pillars which would serve to support the hearths. It has, therefore, been customary heretofore to build the hearths in the form of rather flat arches, with the spring lines of the arches located at suitable skewback rings built into the masonry of the rigid shell. The arched hearths have central openings through which the central shaft extends, and additional openings located at suitable points through which the material being treated in the furnace may drop from hearth to hearth.

The hearths are generally constructed of refractory brickwork because of thehigh temperatures prevailing within the furnace, and, as is well known, refractory brickwork lacks great mechanical strength. Heretofore, it has not been unusual to have the weight of a heavy charge of ore, augmented by the weight of the hearth itself, cause the inner courses of masonry comprising the hearth, or even the entire hearth itself to slip downwardly and thus to interfere with the proper operation of the rakes within the furnace. Notably, this was true in those furnaces in which the hearths were spaced close together with only sufiicient clearance between successive hearths to permit eflicient operation of the rakes. In such furnaces, a hearth displaced downwardly would interfere with the movement of the rakes on the hearth below, and cause a decrease in the efiiciency of the raking on the displaced hearth.

To a considerable extent these difficulties have been overcome by increasing the mechanical strength of the hearths and of the rigid shell by increasing their thickness, and in some cases by using in the construction of the hearths a brick of special design, such as a step brick.

It has been observed, however, that while slippage can be eliminated in this manner, the hearths continue to flatten. This is attributed 5 to thermal expansion and contraction of the furnace, for it is particularly noticeable in furnaces which are shut down and started in operation at comparatively frequent intervals. It also has been observed that in some cases the hearths do not remain in a substantially horizontal plane, but instead tend to sag near the center on one side of the central shaft and rise correspondingly on the other side of the central shaft, thereby interfering with the operation of the furnace. It is one of the purposes of my invention to overcome these difliculties. This I accomplish by embedding in the hearths a plurality of radially disposed reinforcing beams. At their outer ends, the beams are supported by the rigid shell of the furnace, and at their inner ends they may be interlocked with a segmented or other type of ring embedded in the masonry of the hearth and substantially axially aligned about the central shaft. I may dispense with such a ring, but it is helpful in maintaining the hearth in a substantially horizontal plane.

In case the ring is used, it is sometimes advisable to allow the outer end portion of the reinforcing beams to be non-rigidly supported by the rigid shell, for otherwise thermal contraction and expansion of the beam may set up stresses and strains within the hearth, and thereby tend to crack the masonry of the hearth. When the ring is not used, however, it may prove advantageous to fasten the reinforcing beam to the rigid shell, or to the surrounding metallic cylinder in order to assist in the support of the hearth. If the operative means of establishing such a connection between the beams and the 49 rigid shell is sufficiently flexible, it is possible to utilize this connection even in those cases where the ring is also employed.

Preferably the reinforcing beam is curved in such a manner as to conform with the curve of the arch of the hearth, but this is by no means essential. Otherwise the shape of the beam is of no great consequence, so long as it is properly designed to have sufficient mechanical strength and to efficiently perform its function of par- 50 tially supporting the hearth. I find that if the cross-section of the beam is substantially in the shape of an I-beam, these requirements are adequately fulfilled. Likewise, the beam may be made of any material capable of insuring the proper degree of rigidity, and of withstanding the temperatures to which it is exposed. I have found that cast iron is satisfactory for this purpose.

I prefer to make each of the rings in a plurality of segments, the end portions of which are provided with means whereby the segments may be interlocked to form a complete ring. In this manner, it is possible to compensate for differences in the coefiicient of thermal expansion of the material from which the ring is made and of the masonry of the hearth. Suitable lugs are mounted upon the outer surface of the ring in order to receive the inner end portion of the reinforcing beams and thereby flexibly to interlock the beams with the ring. I have found that cast-iron is a suitable material for the ring, but other suitable materials may also be used.

The invention will be better understood from a consideration of the following description in conjunction with the accompanying drawings, in which Fig. 1 is a sectional view of a multiple hearth furnace comprising a plurality of reinforced masonry hearths and embodying my invention;

Fig. 2 is a plan view taken substantially along the line 22 of Fig. 1, showing one of the inrakinghearths of the furnace;

Fig. 3 is a plan view, taken substantially along the line 3-3 of Fig. 1, showing one of the outraking hearths of the furnace;

Fig. 4 is a side elevation of a reinforcing beam embedded in a hearth and fastened at its outer end to the metallic cylinder surrounding the rigid shell of the furnace;

Fig. 5 is a side elevation of a reinforcing beam embedded in a hearth and non-rigidly or loosely supported at its outer end by the rigid shell of the furnace;

Fig. 6 is a side elevation of a reinforcing beam embedded in a hearth and having its inner end portion interlocking with a ring embedded in the hearth;

Fig. 7 is an end elevation of the beam shown in Fig. 4;

Fig. 8 is a sectional elevation of a reinforcing beam of preferred design;

Fig. 9 is a plan'view of a quadrant of a ring of preferred design;

Fig. 10 is an elevation of the ring quadrant shown in Fig. 9;

Fi 11 is a sectional view taken substantially along the line of Fig. 9 and showing a lug suitable for interlocking the inner end portion of a reinforcing beam witharing; and

Fig. 12 is a sectional view taken along the line |2 |2 of Fig. 11 showing in cross-section a ring of preferred design.

In Fig. 1 is shown a roasting furnace comprising a plurality of hearths located within a rigid shell 20, which is surrounded by a metallic cyl inder 2| Out-raking hearths 22 and in-raking hearths 23 are arranged alternately one above the other. A rotatable, hollow central shaft 24 is centrally located within the rigid shell, and radially mounted thereon are a plurality of rakes 25, so arranged in tiers that, as they rotate with the central shaft, they cause an outward movement of the ore being treated on the out-raking hearths and an inward movement of the ore being treated on the in-rakinghearths. The ore being treated drops from the in-raking hearths 23 to the out-raking hearths 22 through openings 26, located in the in-raking hearths near the central shaft, and from the out-raking hearths 'to the in-raking hearths through openings 27 located in the out-raking hearths near the rigid shell 20.

The hearths 22 and 23 are constructed of step bricks 28 in the form of an arch, the spring line of which is located at suitable skewback rings 30. The skewback rings form the support for the arched hearths.

Figs. 1, 2 and 3 show the reinforcing beams 3| of the invention embedded in the hearths. As indicated in the drawings, these beams are non-rigidly supported at their outer ends by the rigid shell 20, and at their inner ends are interlocked with rings 32, one of which is embedded in each hearth andis substantially axially aligned about the central shaft.

The step bricks from which the hearths are constructed will prevent the inner course of masonry from slipping downwardly below the outer courses of masonry, but they will not prevent the flattening of the arch induced by thermal contraction and expansion of the hearth. The tendency of the arch to flatten, however, is prevented by the reinforcing beams, in a manner that will be understood by one skilled in the art.

The rings 32 with which the inner end portions of the reinforcing beams are interlocked, may be eliminated from the structure, but their use is advisable, for they will aid in maintaining the central portion of the arched hearth in a substantially horizontal plane.

Figs. 4 to 14 show in some detail my preferred design of reinforcing beams and supporting rings.

Fig. 4 shows a reinforcing beam 3| in elevation. The outer end portion 33 of the beam is supported by the rigid shell 20, and is fastened in a manner to be described to the metallic cylinder 2| surrounding the rigid shell. In Fig. 5 is shown a reinforcing beam 3| the outer end portion 34 of which is supported by the rigid shell 20. but which differs from the beam shown in Fig. 4 in that the outer end portion 34 of the beam is not fastened to the metallic cylinder 2|. Fig. 6 shows a reinforcing beam 3|, in all respects similar to the beam shown in Fig. 5, the outer end portion of which is supported by the rigid shell 20. The inner end portion of the beam is shown in Fig. 6 as interlocked with the ring 32 embedded in the masonry of the hearth. In each of the aforementioned figures I have shown beams 3| curved substantially to conform to the curvature of the arch of the hearth in which they are embedded. The outer end portions 33 and 34 of the beams are bent at an angle to the curved portions of the beams, and are substantially straight.

-In this manner, I produce a beam which will rest substantially horizontally on the support provided by the rigid shell 20, and yet which will conform to the curved arch of the hearth in which the beam is embedded.

60 When fastening the outer end portion of the beam to the metallic cylinder surrounding the rigid shell, as shown in Fig. 4, I make the substantially straight outer end portion 33 of the beam of suflicient length to extend through the rigid shell 20 to a point exteriorly of the metallic cylinder 2|. The outer end portion 33 of the beam is then anchored by means of a U-bolt 35 to the metallic cylinder, as shown in Figs. 4 and '7. The cross-bar of the U-bolt passes over the upper surface of the beam, and the prongs of the U-bolt extend substantially vertically downwardly, along the sides of the beam, and through holes provided in a horizontally extending portion of an anchor plate 36. The anchor plate preferably comprises a heavy metallic angle, one side of which is rigidly fastened to the outer surface of the metallic cylinder 2| in any suitable manner, as by welding, and the other side of which extends substantially horizontally and outwardly from the outer surface of the metallic cylinder. The end portions of the prongs of the U-bolt are threaded, and nuts 31 are turned on the threaded portion until they are firmly set against the under surface of the horizontally extending portion of the anchor plate 36. In this manner the reinforcing beam may be firmly anchored to the metallic cylinder 2|, and be held rigidly against the supporting surface of the rigid shell 20. If desired, the U-bolt 35 may be disposed with its prongs projecting upwardly and operatively connected to an anchor plate similar to the plate 36 disposed above the beam 33. I

Although the cross-sectional design of the reinforcing beam may be varied within wide limits, it being only necessarythat the beam possess sufficient mechanical strength to prevent a fiattening of the arch, I prefer to make the beam with a cross-section substantially that of an L beam. The cross-section of a beam of my preferred design is shown in Fig. 8.

The ring with which the inner end portion of the re-inforcing beams may be interlocked is preferably made in a plurality of segments in order to allow for a difference in the coefficient of thermal expansion of the metal comprising the ring and the masonry of the hearth in which it is embedded. Any convenient number of segments may be employed. In Fig. 9 is shown one segment 40 of a ring comprising four segments.

The segment is in the shape of the quadrant of a circle, and at either extremity of the segment are a plurality of teeth 4| so arranged that when the ends of two segments are brought together, the teeth of one segment will slip into the recesses 42 between the teeth of other segment, thereby flexibly interlocking the two adjacent segments and forming (when four segments in all are used) one half of the ring. Two such halves brought together and interlocked in the manner described comprise the entire ring.

In order that the inner end portion of the reinforcing beams may interlock with. the ring, a plurality of lugs 53, corresponding in number to the number of reinforcing beams used in one hearth, are mounted upon the outer surface of each segment 40 of the ring. Each of these lugs, as shown in Fig. 11, comprises two side pieces 44 extending outwardly from the outer surface of beam into the recess 45, the beam is flexibly interlocked with the segment of the ring.

A cross-section of the segment 40 of the ring is shown in Fig. 12. Preferably the depth of the ring is greater than its thickness, and I find it to be advantageous if an inwardly projecting lip 46 is mounted upon the inner surface of the ring adjacent the underside thereof. This lip serves to support the courses of masonry disposed between the ring and the central shaft of the furnace, as may be seen from Fig. 6.

Cast-iron is a suitable material for the reinforcing beams and for the ring. This material is well adapted to withstand the temperatures likely to be encountered within roasting furnaces. It is cheap, and it may readily be cast into beams and segments of rings. the segments of the rings are made from this or any other cast material, it is possible to make the ring 40, the teeth 4|, the side pieces 44 of the lugs, and the lip 45 in one integral casting.

Although I have herein described preferred embodiments of my invention, it is to be understood that various modifications may be made by those skilled in the art without departing from the spirit of the invention.

I claim:

A multiple hearth furnace comprising a rigid shell, a central shaft disposed within the rigid shell, a plurality of masonry hearths disposed between the rigid shell and the central shaft, a

When v metallic ring embedded in each hearth and subend portions non-rigidly supported by the rigid shell and their inner end portions non-rigidly connected to the ring. WILLIAM J. THOMAS. 

